This project is designed to study and compare the microstructures of copper rich dental amalgam systems. Eight copper rich systems have been studies and three more are in progress. All copper rich systems have the gamma 1 (Ag-Hg) matrix phase of conventional amalgam as well as residual alloy particles. The weak, corrosion prone gamma 2 (Sn-Hg) phase is greatly reduced or eliminated and is replaced by copper-tin phases. Gamma 2 forms initially in most cases and gradually disappears with time after condensation. The nature of the new phases is being studied. The corrosion products of both conventional and copper rich amalgams are being studied in chloride and sulfide solutions. Scanning electron microscopy and energy dispersive x-ray analysis are used to study the microstructure and chemical compositions. X-ray diffraction is used to study the nature and quantities of the phases in the amalgams as well as to identify the corrosion products.